Thermographic copy paper and process



Oct. 9, 1962 D. A. NEWMAN ETAL 3,057,999

THERMOGRAPHIC COPY PAPER AND PROCESS FiledI March 51, 1960 INV EN TORS ougl as A /Vewma/v BYZZa n T 56k/ot z/zaud' ATTO/@VE YS Patented Oct. 9, 1962 3,057,999 THERMUGRAPHC COPY PAPER AND PROCESS Douglas A. Newman, Glen Cove, and Allan T. Schlotzbauer, Locust Valley, NZ., assignors to Columbia Ribbon and Carbon Manufacoiring Co., Inc., Glen Cove,

NX., a corporation of New York Filed Mar. 3l, 1960, Ser. No. 19,048 5 Claims. (Cl. Z50- 65) The present invention is concerned with the preparation of novel heat-sensitive copy sheets and the thermographic process of preparing copies therewith. This application is a continuation-in-part of our copending application Serial No. 419,811, iiled March 30, 1954, now abandoned.

It is known to prepare heat-sensitive copy sheets containing unreacted chemical compounds which react under the inliuence of heat to form a colored composition. Such sheets are used for instance in a thermographic machine whereby they are placed beneath an original sheet which it is desired to copy. The combination is then subjected to infrared radiation within the machine so that the images on the original sheet absorb the infrared radiation, convert it to heat and thus warm Ithe copy paper in only the predetermined areas which correspond to the imaged areas of the original sheet. Such copy sheets have decided disadvantages in that the chemicals which can be used successfully are rather limited and rather expensive, Also, the required temperature of reaction and color formation appears to be quite limited and critical, slight variations causing unreliable copy.

It is also known to prepare heat-sensitive copy sheets comprising a colored foundation sheet bearing a normally opaque blushed coating. Thus the copy sheet has a White or gray appearance prior to use, but under the influence of heat generated in the thermographic process as above, the selectively heated areas of the blushed coating are melted and become transparent, thus allowing the color of the foundation sheet to show through in the areas corresponding to the imaged areas of the original. Such sheets have many important disadvantages. For instance, since they depend upon the foundation sheet color becoming visible through the blush coated layer, then the thickness and melting point of such layer must be very closely controlled within narrow ranges. For this reason also, such sheets are very sensitive to the touch and even casual contact results in unintended smudging and marking of the sheets. Likewise, since these sheets require the use of colored foundation sheets, they are rather expensive and have an unpleasant appearance. Also, due to the extreme sensitivity of the blush coating on the foundation sheets, their use is limited to the production of sharp copies of only one-sided original sheets, i.e. sheets having imaging on only one side.

It is an object of the present invention to prepare novel heat-sensitive copy sheets which are relatively inexpensive and which may be used over a wide range of temperatures without any appreciable difference in tone strength.

It is another object of the present invention to prepare heat-sensitive copy sheets which may be used to prepare faithful copies of either oneor two-sided original sheets.

It is still another object `of the present invention to prepare blush-coated copy sheets in which the blush coating provides its own color independent of the color of the foundation sheet.

These and other objects are accomplished according to the present invention as set forth herein.

In the drawings:

FIGURE 1 is a fragmentary cross-section, to an enlarged scale, of a copy sheet according to the present invention.

yFIG'. 2 is a fragmentary cross-section, to an enlarged scale, of an original sheet and a copy sheet in one arrangement prior to irradiation.

FIG. 3 is a fragmentary cross-section, to an enlarged scale, of an original sheet and a copy sheet in a second arrangement particularly adapted to the copy of twosided original sheets.

FIG. 4 is a fragmentary cross-section, to an enlarged scale, of the original sheet and copy sheet arranged as in FIG. 2 but after irradiation.

The thermographic manifolding sheets and process of making the same of the present invention obviates the inherent disadvantages of the old methods in that it requires only a single coating without any chemical reactants therein and does not require any specially prepared paper. The paper yaccording to the present invention is preferably white, but may be any color, or even transparent or semi-transparent, as for instance parchmentized paper, because the marking is not dependent upon the color of the backing material but upon the coloration of the coating, as more clearly brought out hereafter.

This is accomplished in the present invention by the coating of a desired foundation sheet with a spongy, heatcompressible coating having non-infrared radiation-absorbing material so dispersed throughout as to present a light tint or hue of the undispersed material and which when compacted under the influence of the heat generated by the imaged areas of the original produces a distinguishable dense color value of the color.

The nature of the pigment or dye used in the spongy layer is most critical to the present thermographic process. It is essential -that the colorant be relatively immune to infrared radiation since the absorption of such radiation brings about heat generation in the absorbing body with attendant melting and cohesion of the surrounding spongy layer. Thus, if infrared radiation-absorbing pigment or dye were used in the present copy sheets, then the entire spongy layer would melt and cohere and the areas corresponding to the imaged areas of the original would be indistiguishable from the remainder of the sheet.

Such a heat markable coating we have found may advantageously comprise a substantially heat-cohesive resin dissolved in a volatile, rapidly evaporating medium which is combined with an essentially immiscible, slower evaporating fluid and having water-insoluble pigment particles or other suitable dyestui coloring material dispersed therein. The resulting emulsion, when applied to a base web or sheet and thereafter dried, resu'lts in a cellular compressible residue forming a coating and having the pigment particles or coloring material dispersed therein in uncompacted relation. Usually it is preferable to have the coating generally opaque and showing a light tint of the color value of the coloring material. When infrared heat is applied, as generated by the imaged areas of the original sheet, the cell structure of the coating is melted and broken down and compressed so that the coloring material is compacted on the surface of the sheet, and thus produces a mark which is the stronger color value of the color in the lightly tinted opaque unmelted and uncompressed coating which remains the background on which the mark is clearly visible.

A feature of this invention is the provision of a manifold sheet having a non-tacky, chemical-free coating which is normally non-transferable and non-markable in ordinary handling and yet which is highly heat-sensitive and when subject to such heat will be compressed and produce a contrasting mark.

FIG. l of the drawing represents a crosssection of a manifold sheet made in accordance with this disclosure showing, in diagrammatic and enlarged form, the cellular structure and pigment or dye particles in the coating.

FIGS. 2-4 represent cross-sections of a manifold sheet and an original sheet, in diagrammatic and enlarged form, during and after exposure to infrared radiation.

We have found that those film-forming resins which are highly cohesive and which tend to have more cohesion than `surface adhesion for other materials or articles when dry and are capable of being dissolved in low boiling point, rapidly evaporating solvents are satisfactory for carrying out this invention. Such materials are the usual resinous binders such as used in lacquers or the like. According to the present invention, it has been discovered that these resinous materials can be altered in their physical properties to form a cellular compressible coating which is capable of retaining pigment particles dispersed therein on or in the cell-like wall structure in a `separated uncompacted condition. The alteration in physical properties can be brought about, it has been dis covered, by selecting and adjusting the suspending liquids during the preparation of the coating. At least two different liquids kare used, one being la solvent for the ybase material and the other being a non-solvent therefore at normal working temperatures. The liquids are of a volatile nature to the extent that they may be driven oit the applied coating by evaporation. In most instances said non-solvent liquid is water and has an evaporation rate substantially lower than that of the solvent. The liquids used must be essentially immiscible `and capable of forming an emulsion. The solvent liquid is usually an organic solvent having a fairly high evaporation rate and is generally used in amounts substantially in excess of the amount of non-solvent liquid present. The solid base material is selected so as to be soluble in that portion of the liquid which is regarded as the solvent. The solvent may be carbon tetrachloride used singly or together with acetone which increases the solubility rate of the solvent to dissolve the resin, such as ethyl cellulose. The emulsion thus formed is a heterogeneous mass including a discontinuous phase of water globules enti-tapped in the resinous continuous phase.

In practice lit has been found that since the ethyl cellulose is more readily dissolved in acetone, it is preferable to initially dissolve the ethyl cellulose therein. The carbon tetrachoride which is miscible with the ethyl celluoseacetone soution is then added thereto.

The mixture of solid base material and its solvents are colored by the inclusion of a suitable water-insoluble pig ment in proper proportions dispersed `in the emulsion. While a wide variety of waterainsoluble pigments may be used, especially good results thus far have been obtained from a blue lake pigment.

An example of a coating mixture made according to the present invention and one which is presently preferred is given by the following formula:

Ingredients: Parts by weight, grams Ethyl cellulose 9 Acetone 4l Microcrystalline Be square wax 4 Carbon tetrachloride 50 20% blue lake dispersion l2 Water It is to be noted that the above coating mixture includes microcrystals of Be square wax manufactured by the Bareco Oil Company. However, such substance is not necessary to the formation of the `desired coating. The Be square wax has the function of a plasticizer, and thus `it is readily apparent that the proportion of Wax used is determined by the amount of pliability or workability desired of the coating or if not found necessary may be omitted entirely, or any other suitable plasticizer or softening material may be used. Likewise, where lit is desired to increase the hardness and resistance to unintended pressure-marking of the blush coating, small amounts of other materials may be added to the thermoplastic resin. Such materials should be compatible with the basic resin, such as ethyl cellulose, and should also be soluble in the solvent used for the application of the blush coating. Suitable materials for this purpose are vinyl resins such as Vinylite VYSG and VYLF, Zein, `shellac, etc.

The ingredients of the mixture set forth in the above example are thoroughly intermixed in the following manner: the ethyl cellulose is initially dissolved in the acetone, then intermixed with the carbon tetrachoride carrying the optional dissolved Be square wax. The 20% blue lake dispersion is then added to the water. The ethyl cellulose solution containing the solvents of acetone and carbon tetrachloride is then mixed into an emulsion with the water containing the blue lake dispersion. The resulting emulsion is spread in a thin uniform coating on a flexible foundation such as a web of paper or other type of sheet and allowed to dry by evaporation of the liquid constituents. In the operation of the mixture of this character, as presently understood, it is thought that the resin base, ethyl cellulose in the above example, by being dissolved in the solvent has the immiscible but non-solvent `liquid distributed in globules through itself. As the coating begins to dry, it appears that the solvent in evaporating more rapidly forms a matrix of partially solidified base material about the more slowly evaporating globules of water. When the watei evaporates through the drying process, the matrix is suihciently strong to retain its shape and thereby form cell-like vacuities. The pigment appears to be entrapped within the solidified resin or on the walls of the cells when the water has evaporated. lt is evident, however, that the pigment particles are dispersed and separated throughout the coating by the cellular structure of said coating. The cellular structure is somewhat analogous in appearance to a honeycomb when viewed under a microscope.

FIG. l of the drawing illustrates on a larger scale a schematic View of the coating 10 as applied to a base web 12, the liquid medium having been evaporated therefrom. The figure is intended to show 'a possible arrangement of the cell structure 13 and the pigment or dye particles 14 before and after heat cohesion has occurred. The two extremities 1S show the cellular structure 13 with the pigment particles 14 dispersed therein in a separated and uncompacted relation. When viewed, the uncollapsed coating is opaque and has a light tinge below the range of color value of the pigment because of the light refraction through the vacuities 16 of the cell structure. The central portion `17 of the figure illustrates the structure after infrared heat has been locally applied. The cells 13 have been completely collapsed and the pigment particles 14 which were initially separated by the cell structure are now compacted and arranged in more or less abutting and overlapping relation so that when viewed they will have substantially the color value of the pigment particles.

FIGS. 2 and 3 of the drawing show the copy sheet of the present invention comprising a foundation sheet 12 and a spongy blushed coating 1t) placed together with an original sheet comprising a foundation sheet 20 and images 21 prior to being treated with infrared light. The assembly of FIG. 2 is preferred where it is desired to make a copy of -an original sheet which has images 21 on only one side of the sheet, whereas the assembly. of FIG. 3 is preferred where the original sheet has images 21 and 22 on both sides. As shown by FIG. 3, the images 21 on the upper side of the original are in contact with the copy sheet. These images, being closer to the infrared source and being in contact with the copy sheet, selectively are reproduced on the copy sheet in preference to the images 22 on the reverse side of the original.

FIG. 4 of the drawing shows the original sheet and the copy Isheet after infrared irradiation demonstrating the melted and cohered areas 17 which correspond with the imaged areas 21 of the original.

The utility of the present blush-coated sheets in preparing copies by thermographic means relies upon the fact that concentrated heat will reduce the porous layer to a continuous or compact layer, thus concentrating the pigment which was dispersed in the porous structure.

Therefore, when an original sheet having images thereon containing infrared radiation-absorbing pigment or dyestutf, such as carbon black or nigrosine, is placed together with the present blush-coated copy sheet and subjected to infrared radiation, such radiation is absorbed by the images on the original and converted to heat. The original sheet lthus becomes a heat pattern whereby the copy sheet is selectively heated in areas corresponding to the imaged areas of the original. This selective heating results in a pigment concentration in these areas thus producing an exact copy of the original sheet.

The source of infrared radiation is not particularly critical although it has been found convenient to employ devices such las the Thermo-fax machine or a flat bed thermograph apparatus, both of which rely upon infrared lamps as the radiation source. The time of exposure depends upon the strength of the radiation source as well as the melting point of the porous layer, but in general an exposure for between two and twenty seconds is suiicient. In this manner, temperatures between about 150 F. to 650 F. are generated vin areas of the porous layer to cause them to fuse or melt and destroy the porous structure, thus resulting in preselected pigment concentration.

It should be understood that although ethyl cellulose is the preferred resin component, other thermoplastic resin materials may be employed in place thereof. Among such materials may be mentioned the cellulose esters such as cellulose acetate and cellulose nitrate; cellulose ethers such as benzyl cellulose and glycol cellulose; and unsaturated polymers such as polymethyl methacrylate yand polystyrene. It `is important that the melting point of the porous resin composition be sufficiently low to insure heat-compression of the layer. Thus, where necessary, known plasticizers may be added to the resin to lower the melting point within the operating range of from about 100 F. to about 350 F.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

We claim:

1. A self-marking heat-sensitive copy sheet comprising a foundation sheet having thereon a cellular heat-compressible coating having so dispersed therein particles of non-infrared radiation-absorbing coloring matter as to present a weak or light tint of the true color of the coloring matter, the cell structure of which coating melts and compresses under the influence of heat causing the particles to concentrate and present the true dense color of the coloring matter.

2. A self-marking heat-sensitive copy sheet comprising a foundation sheet having thereon a cellular heat-compressible coating containing a thermoplastic resin and having so dispersed therein particles of non-infrared radiation-absorbing coloring matter as to present a weak or light tint of the true color of the coloring matter, the cell structure of which coating melts yand compresses under the inuence of heat causing the particles to concentrate and present the true dense color of the coloring matter.

3. A self-marking heat-sensitive copy sheet comprising a foundation sheet having thereon a cellular heat-compressible coating containing ethyl cellulose and having so dispersed therein particles of non-infrared radiation-absorbing coloring matter as to present a weak or light tint of the true color of the coloring matter, the cell structure of which coating melts and compresses under the inuence of heat causing the particles to concentrate and present the true dense color of the coloring matter.

4. The method of producing a duplicate copy exactly corresponding to an imaged original sheet through the use of a copy sheet having thereon a cellular heat-compressible coating having so dispersed therein particles of noninfrared radiation-absorbing coloring matter as to present a weak or light tint of the true color of the coloring matter the cell structure o-f which coating melts and compresses under the influence of heat causing the particles to concentrate and present the true dense color of the coloring matter, which comprises superposing said original sheet and said copy sheet and subjecting said sheets to infrared radiation for a period of time sufficient to allow the coating on the copy sheet to compress in areas corresponding to the imaged areas of the original sheet, and separating the sheets to produce the duplicate copy.

5 The method according to claim 4 in which the heatcompressible coating contains ethyl cellulose.

References Cited in the file of this patent UNITED STATES PATENTS 2,740,896 Miller Apr. 3, 1956 2,880,110 Miller Mar. 3l, 1959 2,919,349 Kuhrmeyer Dec. 29, 1959 2,940,866 Sprague et al June 14, 1960 2,950,987 Howard Aug. 30, 1960 2,967,785 Allen et al Ian. 10, 1961 

